Apparatus for manufacturing a surgical suture

ABSTRACT

An apparatus for melt fusing a length of multifilament thermoplastic surgical suture includes a radiant heater having a two part longitudinally divided tunnel. A length of multifilament material is advanced into the tunnel and is held in a stationary position under tension while being fused.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus for melt fusing a suitable controlled length of a multifilament thermoplastic surgical suture. The melt fusion essentially seals and stiffens at least one end of the suture. This invention also relates to an apparatus for cutting at least one end of a surgical suture.

Most braided suture material, for needled and non-needled products, is skeined onto a frame, `dipped` in a polymer resin solution, oven dried, cut off from the frame, and sorted for faulty lengths.

This operation is slow and messy, labor intensive and space consuming, and all that is achieved is the cutting of the sutures to length, the sealing of the ends to prevent fraying, and stiffening for greater ease of insertion into a needle. The average product spends 2 days of in-process time in the end dipping department.

This invention eliminates the end dipping operation for braided thermoplastic suture materials, and replaces it by an inline system in the next production operation (viz. needle attaching, or winding in the case of non-needled sutures) with a reduction of in-process time and floor space requirements.

For braided thermoplastic suture materials heat is used to achieve melt fusion of the outer filaments of the braid.

The braid is handled from the reel or spool as a controlled, continuous strand. Following melt fusion of the desired section of braid, it is cut to the required suture length and ready for additional processing.

SUMMARY OF THE INVENTION

An apparatus for melt fusing a suitable controlled length of a multifilament thermoplastic surgical suture has been invented. The invention comprises a heater and means for tensioning the length of the filaments being fused. In one embodiment, the heater is selected from the group consisting of an infrared, microwave and ultrasonic heater. In another embodiment, the heater is an electrical resistance radiant heater.

In still another embodiment, the heater is an electrical resistance radiant and convection heater having a split cylindrical tunnel. In a specific embodiment, the temperature of the heater is in the range of about 100° to 500° C. In a more specific embodiment, the temperature is in the range of about 200° to 400° C. In another specific embodiment, the means for tensioning comprises a first and second means for guiding the suture. The first and second means being adjacent the respective proximal and distal ends of the heater. In another more specific embodiment, the first guiding means comprises a means of producing a controlled frictional drag on the suture. In a most specific embodiment, the second guiding means comprises a means of producing a variable angular velocity.

In still another more specific embodiment, the first and second guiding means comprise respectively a first and second means of producing a variable angular velocity, with the proviso that the angular velocities from the first and second producing means are different.

In yet another embodiment, the thermoplastic in the surgical suture is selected from the group consisting of a polyester, a polyamide, and a polyolefin. In a specific embodiment, the polyester is a poly(glycolic acid). In a more specific embodiment, the poly(glycolic acid) is a homopolymer. In another more specific embodiment, the poly(glycolic acid) is a copolymer.

An apparatus for cutting at least one end of a surgical suture has also been invented. The invention comprises means for inserting the suture through an opening; means for tensioning at least the portion of the suture adjacent to the opening; and means for shearing the suture. In one embodiment, the apparatus also comprises means for moving the shearing means across the opening. In a specific embodiment, the shearing means comprises a cutting blade.

In another embodiment, the plane of the shearing means is about fifty to eighty degrees from the axial centerline of the suture. In a specific embodiment, the plane is about sixty to seventy degrees from the axial centerline. In yet another embodiment, the plane of the cutting blade is perpendicular to the axial centerline of the suture.

In yet another embodiment, the surgical suture comprises a multifilament. In still another embodiment, the surgical suture comprises a monofilament.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the prior art steps for end dipping and needling a suture;

FIG. 2 is a graph showing the relationship between suture size and melt fusion temperature;

FIG. 3 is a schematic view showing the apparatus for melt fusing and cutting a suture end; and

FIGS. 4 and 5 are broken front and cut away side views, respectively, of the cutting apparatus of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The overall system control as well as the individual process operations may be attained, in an automated fashion, by several means. In the preferred embodiment of this invention, the following are the means of choice:

1. The system is monitored and controlled by means of a microcomputer or a programmable logic controller (PLC).

2. Thermal `sealing`/stiffening of thermoplastic braid suture materials is performed by melt-fusion of the outer filaments using radiant/convective (i.e. non-contact) heater blocks. When closed, the blocks form a straight tunnel of circular cross-section to provide the braid with uniform thermal exposure around its entire periphery. When the braid is advanced/indexed the blocks open in order to minimize the thermal exposure of the main suture body which is to be left untreated.

3. Braid advancement and suture length control is achieved by means of one or more pairs of apposed, elastomer-foam coated, friction rollers that are driven by a stepper motor. This provides accurate length control under moderate, controlled tension, for a wide range of braid diameters, without abrasive damage.

4. Suture presence and knot detection is accomplished using adjustable intensity/sensitivity, through-beam optical sensor pairs.

5. Straight or bias cutting, without distortion of the braid cross-sectional shape is performed using an automatically actuated razor blade. It shear cuts across a hole in an anvil plate through which the braid protrudes.

Several of these means are described in greater detail below.

SUTURE THERMAL EXPOSURE

The appropriate treatment temperature and time for the braided suture in the heating tunnel varies according to the suture material and diameter. FIG. 2 shows the heating temperature versus optical braid diameter for a silicon coated polyester braided suture at an exposure time of three (3) seconds.

The exposure temperature and/or time must be increased with an increase in diameter of any given material. The required exposure temperature set point also varies directly with the heater tunnel diameter but is inversely related to the exposure time. Keeping all other parameters constant, there is a temperature range below which there is insufficient heat (radiation) in order to achieve any melting at all of the outer filaments, or above which there is almost total melt/fusion of the entire cross section of the suture material. For example, for a 4 mm diameter heating tunnel the temperature range would be about 260° C. to 300° C. for such as a size 2/0 silicone coated polyester suture on a 3.0 second cycle.

MELT FUSION OF OUTER FILAMENTS

1. Initial Melting Action

The loose outer filaments that protrude from the basic outer diameter of the braid are initially melted back to the true outer diameter by the radiant heat. While this is not the same as the open flame singeing process commonly used for silk sutures, it does achieve the same result. The initial melting of loose filaments reduces or eliminates the resistance to an easy insertion into the needle's drilled hole.

2. Surface Filament Melt Fusion

After the initial melting of the protruding filaments, the material temperature rises enough to commence the melt fusion of the outer surface of the outer filaments. Note that only a small percentage (estimated to be 5-10%) of the outer filaments actually undergo surface melting and fuse with adjacent filaments at the respective contact points. FIG. 2 is a graph showing the relationship between USP (United States Pharmacopoeia Convention, Inc., MD U.S.A.) suture sizes and melt fusion temperatures.

Hence the suture stiffens on cooling but with only a comparatively small loss in strength. This melt fusion of the outer filaments has the effect of both:

a. Holding the filaments together when the stiffened section is cut, avoiding the brooming that would otherwise occur.

b. Stiffening the suture for ease of control and insertion into the drilled hole of a needle.

SUTURE END STIFFNESS

The stiffness of the heat treatable sutures can be increased by either:

a. increasing the temperature of the heating tunnel, or

b. by reducing the diameter of the heating tunnel, or

c. by increasing the dwell time in the tunnel.

Table I shows the flexural stiffness measurements for USP size 3/0, silicone coated polyester braided sutures that have been heat stiffened at 260° C. (setpoint) for 3 seconds. The measurements were made using a Karl Frank Bending Stiffness Tester (Model No. 58963, Karl Frank GmbH, Weinheim-Birkenau, W. Germany). The higher measured stiffness of the heat stiffened sutures, as contrasted to the end-dipped ones, of Table 2, provides for ease of suture insertion into drilled end needles. This degree of stiffening is obtained with less than approximately 10% reduction in suture tensile strength. Higher or lower stiffness may, of course, be obtained as described above.

SUTURE DIAMETER REGULATION

In the current embodiment of this invention, the diameter of the stiffened suture section is regulated by controlling the braid tension during heating. Normally it is desired to maintain approximately the untreated suture diameter. While the stiffened end must be easily insertable into the standard drilled end needle, its diameter must not be reduced to the point of decreasing the needle attachment strength obtainable after swaging. The tension (during heat stiffening) required to achieve this varies with suture size, construction, material and previous thermal/drawing history. As indicated in Table 1, the appropriate heating tension for this particular example is approximately 40 to 80 g. Higher tensions during heating, generally cause a stretching of the braid with a concurrent reduction in diameter. Lower tensions, or free feed operation allows the braid to shrink axially and increase in diameter.

Table 2 shows the contrasting stiffness values for a prior art end-dipped suture.

                  TABLE 1                                                          ______________________________________                                         STIFFNESS                                                                      (Units = mN at 1 mm Suture Length)                                             Material = Silicone Coated Dacron Suture                                       Size = USP 3/0                                                                 PROCESS PARAMETERS:                                                            TEMPERATURE SETPOINT =    260° C.                                       EXPOSURE TIME =           3 Sec.                                               BRAID TENSION =           40-80 g.                                             HEATER TUNNEL DIAMETER =  4 mm                                                 Sample No.   HEAT STIFFENED                                                    ______________________________________                                         1            200                                                               2            219                                                               3            203                                                               4            250                                                               5            221                                                               6            195                                                               7            220                                                               8            233                                                               9            217                                                               10           253                                                               11           219                                                               12           218                                                               13           204                                                               14           235                                                               15           186                                                                            Avg. = 218                                                                     S.D. = 18                                                         ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         STIFFNESS                                                                      (Units = mN at 1 mm Suture Length)                                             Material = Silicone Coated Dacron Suture                                       Size = USP 3/0                                                                            END-DIPPED IN                                                       Sample No. POLYMER RESIN SOLUTION*                                             ______________________________________                                         1          46                                                                  2          33                                                                  3          37                                                                  4          39                                                                  5          34                                                                  6          35                                                                  7          38                                                                  8          27                                                                  9          33                                                                  10         39                                                                  11         38                                                                  12         45                                                                  13         34                                                                  14         31                                                                  15         28                                                                             Avg. = 36                                                                      S.D. = 5                                                            ______________________________________                                          *TICRON ™ Suture (American Cyanamid Company, Wayne, NJ 07470 U.S.A.)  

The means used for controlling the braid tension is illustrated schematically in FIG. 3. Upon entering the system a frictional `drag` force is applied to the braid by a spring loaded pair of tension disks. Increasing the compression of the spring with the retainer nut, results in greater disk compression and a higher drag force on the braid. This may alternatively be achieved by any variable electromagnetic disks, mechanical or magnetic clutch or other tensioning device commonly used especially in the textile industry. Maintenance of the braid tension at the other end of the system (i.e. beyond the heater) is achieved by the pair of apposed, elastomer foamcoated friction rollers, one of which is driven by the stepper motor. These rollers are compressed against each other, by a spring or other means to exert a frictional `drag` force on the suture which is advanced between them. This `drag` force is at least equal to that of the tension disks, and usually greater, so that the suture advance may be controlled without slippage of the braid between the rollers.

As an alternative to the diameter regulation means described above in which braid tension is the controlled parameter, it is also possible to firmly clamp the braid at both ends of the heating tunnel and regulate the diameter by controlling the relative motion of the two clamps toward or away from each other. Although this clamp relative motion control is not yet quantified, the following principles are generally observed.

If the clamps are moved inwards, the portion of suture in the heating tunnel increases in diameter. If the clamps are held still when heating, the diameter reduces slightly. In order to maintain a constant diameter during heating, the clamps must move inwards a very small amount.

The amount of movement inwards and outwards in order to, for example, reduce the diameter by 10%, has not yet been established. This is currently being achieved by the controlled tension system described above.

None of the automated systems developed thus far contain a diameter measuring device. An optical sensor or other means may be incorporated in future machines with a feed back control loop.

Any of the diameter regulation means described here may be used in conjunction with the heat stiffening process to provide a number of suture product variants.

One such product is a controlled release suture/needle combination as defined in The United States Pharmacopeia Twenty-first Rev. (hereafter abbreviated as USP), United States Pharmacopeial Convention, Inc., Rockville MD, U.S.A., 1984, Section 871. The lower needle holding strength may be obtained by a greater degree of thermal exposure (i.e. more suture strength degradation) or by reducing, the diameter of the stiffened section during heating by increasing the tension or by moving the clamps apart to stretch the braid.

Another product variant is a suture with a 1:1 needle-to-suture diameter ratio. The stiffened section of the braid is reduced in diameter during heating by using one of the techniques described above. Then, once cut, the reduced diameter end(s) may be inserted into a drilled end needle having essentially the same outside diameter as the main body of the suture. In surgery, the suture will then fill the hole left in the tissue by the needle.

SUTURE CUTTING

The primary objective in cutting the braid after heat stiffening is to obtain non-broomed ends that retain the approximately round cross-sectional shape of the braid. While this may be accomplished by various assemblies that differ in the design details, the concept embodied in this invention will be described here.

The location of the cutting assembly in this system is shown schematically in FIG. 3. One design that has been built and run successfully is shown in somewhat greater detail in FIG. 4.

The new suture cutting technique of this invention achieves the objective described above by means of the shearing action of a razor blade across an anvil plate. The suture is advancd through a tear-drop shaped hole in the anvil plate. The cutting edge of the razor blade is then driven (i.e. sheared) across the hole, in a straight or arcing motion, in such a manner that an acute angle (i.e. generally less than approx. 15°) exists between the edge and its direction of motion. As a result, the edge pushes the braid sideways into the end of the tear-drop shaped hole that has the smallest radius of curvature. With the contour of the braid supported by the hole in this way, further motion of the blade cuts the braid with minimal distortion of its shape. If the anvil plate, and therefore the blade's cutting plane, are perpendicular to the axial centerline of the braid a straight cut is obtained. Alternatively, a `bias` cut may be obtained by inclining the anvil plate to the suture's axial centerline. It has been found empirically, that a bias cut made at an angle of about 60° to 70° to the suture's axial centerline, facilitates insertion into the needle without significant reducing the needle attachment strength. An angle significantly greater than about 70° does little to facilitate insertion into the needle drill hole. An angle significantly lower than about 60° would reduce the length of the suture end that is engaged by the swaged end of the needle, thereby lowering the needle attachment strength.

NEEDLE ATTACHMENT STRENGTH

The needle attachment strength data shown in Tables 3 and 4 indicate an essentially equivalent quality of attachment for the heat stiffened sutures in value for sutures heat stiffened by this invention and by means of end-dipping in a polymer resin solution. Both sets of results are well above the required average minimum of 0.68 kg (as per The United States Pharmacopeia Twenty-first Rev. (hereafter abbreviated as USP), United States Pharmacopeial Convention, Inc., Rockville MO, U.S.A., 1984, Section 871) for this size (i.e. 3/0) suture. The sample Nos. in Tables 1 and 2 are identical.The sample Nos. in Tables 3 and 4 are identical. However, the sample Nos. 1 to 15 in Tables 1 and 2 are not necessarily identical to the sample Nos. 1 to 15 in Tables 3 and 4.

                  TABLE 3                                                          ______________________________________                                         NEEDLE ATTACHMENT STRENGTH                                                     (Units = Kg.)                                                                  Material = Silicone Coated Dacron Suture                                       Size = USP 3/0                                                                 PROCESS PARAMETERS:                                                            TEMPERATURE SETPOINT =    260° C.                                       EXPOSURE TIME =           3 Sec.                                               BRAID TENSION =           40-80 g.                                             HEATER TUNNEL DIAMETER =  4 mm                                                 Sample No.   HEAT STIFFENED                                                    ______________________________________                                          1           1.603                                                              2           1.581                                                              3           1.337                                                              4           1.619                                                              5           1.728                                                              6           1.559                                                              7           1.624                                                              8           1.635                                                              9           1.722                                                             10           1.660                                                             11           1.607                                                             12           1.529                                                             13           1.414                                                             14           1.478                                                             15           1.474                                                             16           1.504                                                             17           1.716                                                             18           1.553                                                             19           1.707                                                             20           1.501                                                                          Avg. = 1.578                                                                   S.D. = 0.106                                                      ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                         NEEDLE ATTACHMENT STRENGTH                                                     (Units = Kg.)                                                                  Material = Silicone coated Dacron Suture                                       Size = USP 3/0                                                                            END-DIPPED IN                                                       Sample No. POLYMER RESIN SOLUTION*                                             ______________________________________                                          1         1.574                                                                2         1.462                                                                3         1.636                                                                4         1.349                                                                5         1.763                                                                6         1.439                                                                7         1.738                                                                8         1.502                                                                9         1.499                                                               10         1.693                                                               11         1.682                                                               12         1.282                                                               13         1.546                                                               14         1.682                                                               15         1.762                                                               16         1.358                                                               17         1.783                                                               18         1.897                                                               19         1.449                                                               20         1.314                                                                          Avg. = 1.571                                                                   S.D. = 0.177                                                        ______________________________________                                          *TICRON ™ Suture (American Cyanamid Company, Wayne, NJ 07470 U.S.A.)  

OVERALL SYSTEM OPERATION

An apparatus of this invention is shown schematically in FIGS. 3 to 5. A pair of feed rollers 1, driven by a stepper motor 2, advance a suture braid 3 until a predetermined length is reached. Braid tension is maintained between these feed rollers 1 and the tension disk assembly 4 by the frictional drag force exerted on the braid at these two locations.

The second pair of friction (take-up) rollers 5 is driven by an electric DC motor or a stepper motor 6. These rollers take up the slack braid beyond the cutting assembly 7.

After the braid 3 is advanced to a predetermined suture length it is stopped. The heater blocks 8 close so that the section of braid to be heat-stiffened is enclosed, without physical contact, in the heater tunnel. Once the required exposure time is reached, the heat blocks 8 reopen and the feed rollers 1 advance the heat-stiffened section to the cutting assembly 7. Generally, the distance from the center of the heater blocks 8 to the cutting line 9 is adjusted to be equal to the desired suture length. This allows the next section of suture braid 3 to be heat-stiffened while the previous one is being cut. With the cut at the midpoint of each treated section of braid, a suture with both ends stiffened is manufactured, suitable for a double-armed product, i.e. having two needles.

Once the braid is cut, the take up rollers complete the advancement of the suture so that an operator may proceed with the next process step, such as needle attachment. Alternatively, the sutures may be collected as a batch for future additional processing.

FIGS. 4 and 5 specifically describe the cutting assembly 7. The cutting blade 13 can be adjusted by screws 14 to provide the desired shearing angle. Also, a spring clip 15 can optionally be placed in the cutting blade bracket 16 to assist in keeping the blade 13 against the anvil plate 12.

Referring further to figures 4 and 5, a pusher 20 acts against a pin 21. The pusher 20 is moveably mounted on a threaded shaft 22, and is activated by an electric motor 25. A block 23 moves against a track 24, thus separating the pin 21 from the shaft 22. The point of contact between the block 23 and the track 24 can be adjusted by a set screw 26.

The pusher 20 acts against the pin 21 until the block 23 contacts the ramp 27. The block 23 then moves against the ramp 27 in approximately a diagonal motion (relative to the horizontal motion of the pusher 20) until the pin 21 clears the top of the pusher 20.

After the pin 21 clears the pusher 20, the blade 13 is forced across the opening 11 by the spring 29. The blade 13 is then arrested by a stationary block 30.

The pusher 20 is then moved down the threaded shaft 22 by the motor 25 and slides under the pin 21. The cycle can then be repeated for the next suture strand 3. As shown in FIG. 3, the cutting assembly 7 is oblique to the axial centerline of the suture braid 3. However, it is to be understood that the base 30 shown in FIGS. 3 to 5 is movable, and therefore the angular relationship of the cutting assembly 7 to the axial centerline of the suture braid can be varied. It is further to be understood that an actual showing of the various angular relationships is not necessary for an understanding of this invention.

Referring again to FIG. 3, if during braid advancement, a knot is detected by a through-beam optical sensor 10, the control system automatically causes the last "good" suture to be completed. It then advances the knot to a position just beyond the heater blocks 8. A new section is then heat-stiffened and the knot is subsequently advanced to just beyond the cut line 9. The take-up rollers 5 serve to aid in pulling the knot through the hole 11 (shown in FIG. 4) in the anvil plate 12 of the cutter assembly 7. The flawed section is then cut and the take up rollers 5 discharge it from the machine to be discarded. The normal process cycle is then repeated for the next "good" suture. 

I claim:
 1. An apparatus for melt fusing a suitable controlled length of a multifilament thermoplastic material comprising a radiant heater having a two part cylindrical tunnel, the tunnel having a longitudinal axis parallel to a direction of advance of a multifilament material, said tunnel being divided along the longitudinal axis; means for advancing a suitable controlled length of said multifilament material into the two part cylindrical tunnel; means for maintaining said suitable controlled length in a stationary position in said tunnel; and means for tensioning said suitable controlled length being fused.
 2. An apparatus of claim 1 wherein said multifilament material is a braided material.
 3. An apparatus of claim 2 wherein the braided material is a surgical suture.
 4. An apparatus of claim 1 wherein the heater is a radiant and convection heater.
 5. An apparatus of claim 4 wheren the heater is an electrical resistance radiant and convection heater.
 6. An apparatus of claim 1 wherein the heater is an electrical resistance radiant heater.
 7. An apparatus of claim 1 comprising means for advancing said length of said material along its longitudinal axis and into said tunnel.
 8. An apparatus of claim 1 comprising means for advancing said length of said material along its longitudinal axis and through said tunnel.
 9. An apparatus of claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 wherein the heater has a temperature in the range of about 100° to 500° C.
 10. An apparatus of clam 9 wherein the temperature is in the range of about 200° to 400° C.
 11. An apparatus of claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 wherein the heater has a proximal and a distal end, and the means for tensioning comprises a first and second means for guiding the suture, the first and second means being adjacent the respective proximal and distal ends of said heater.
 12. An apparatus of claim 11 wherein the first means for guiding comprises a means of producing a controlled frictional drag on said suture.
 13. An apparatus of claim 12 wherein the second means for guiding comprises a means of producing a variable angular velocity.
 14. An apparatus of claim 11 wherein the first and second means for guiding comprise respectively a first and second means of producing a variable angular velocity; with the proviso that the angular velocities from the first and second producing means are different.
 15. An apparatus of claim 11 wherein the multifilament material is selected from the group consisting of a polyester, a polyamide, and a polyolefin.
 16. An apparatus of claim 15 wherein the polyester is poly(glycolic acid).
 17. An apparatus of claim 16 wherein the poly (glycolic acid) is a homopolymer.
 18. An apparatus of claim 16 wherein the poly(glycolic acid) is a copolymer. 